Hello student!

First of all congratulations on securing such a good score in JEE MAINS paper 2. So as you've mentioned your marks in JEE MAINS PAPER 2 is 300 and so if we follow the previous year trends of marks vs percentile, you can expect your percentile at this score to be ~99.91 %ile . It may vary according to factors like:

>>No. of students appearing for paper 2 ,

>>Marks they secure in that paper.

>>Difficulty level of paper

You can expect your rank under AIR 300, well depending upon the above mentioned factors again.

Hope this helps!

GOOD LUCK.